The discovery of highly stable organic peracid molecules is critical to the commercialization of detergent formulations containing peracid bleaches. Such bleaches have recently been discovered which are highly crystalline in nature and have relatively high melting points. Also, it is very important for highly stable bleaches to be prepared in a manner which eliminates, or at least minimizes their contamination from metals. Metals or metal ions are particularly deleterious to peracids as they catalyze the decomposition of the peroxygen group.
Consequently, the detergent industry requires peracids which are highly stable, have high melting points and are conveniently manufactured in large volumes. Because of their high melting points both the peracids and their precursors are typically purified by precipitation or crystallization techniques. Metal ions typically present in the crystallization media become trapped in the peracid crystals and become impurities which reduce the stability of the peracid. The amount of metal ion contamination is directly related to stability of the peracid.
A recent patent, U.S. Pat. No. 4,634,551 to Burns et al describes novel, relatively stable and high melting crystalline amide peracids. Generally, the precursors to these amide peracids, that is, the amido acids, are reported to have been prepared by the reaction of the appropriate acid chloride with the appropriate amine followed by precipitation of the resulting amido acid. Stability of these amide peracids is affected not only by metal contamination but also by the chloride impurity. Attempts to purify the peracid have proven inadequate to economically remove metals and chlorides. Even purification of the amine precursor is not adequate to provide an economical product of sufficient purity for use in preparing the peracid.
The peroxyacids found in U.S. Pat. No. 4,634,551 are represented by the formula ##STR1## where in R.sup.1 is selected from the groups consisting of alkyl, aryl or alkaryl radicals containing from about 1 to about 14 carbon atoms, R.sup.2 is an alkylene group containing from 2 to 14 carbon atoms and R.sup.3 is H or an alkyl, aryl or alkaryl group containing from 1 to about 10 carbon atoms, the total number of carbon atoms being from about 10 to about 20.
There has been a need for an efficient, high volume means of producing the above described amide acid in high purity and with good stability. It has been discovered that one means of efficiently providing the amide acid precurser in high volumes is by a process which first prepares a monoamido ester of a dicarboxylic acid and then converts the ester to a peracid. The monoamido ester is prepared by esterifying a polycarboxylic acid of the formula ##STR2## with a lower alkyl alcohol and then reacting the ester with a mono alkyl amine of the formula EQU RNH.sub.2
wherein R is an alkyl radical having from 1 to 20 carbon atoms and R.sup.2 is as defined above. A mixture of monoamide and diamide is thus produced.
The reaction mixture obtained by the reaction of the ester and the amine is distilled under reduced pressure to selectively remove the monoamide carboxylic acid ester from the reaction mixture. Such a process is described in EP 0 445 096 which is incorporated herein by reference. It has been found that such distillation efficiently separates the desired product of this invention but, the stress of the high temperatures and reduced pressures which are necessary causes color forming bodies of undefined nature to be created. These color forming bodies and a small amount of the diamide codistill with the distilled product in spite of a strenuous three stage distillation process.
Accordingly, there is needed a process for efficiently preparing the fatty peroxyacids or salts thereof having an amide moiety in very high volume and purity particularly with the absence of color forming bodies. In particular, there is needed for a process which permits lower distillation temperatures, thus reducing the thermal stress on the desired product while providing high product purity without the loss of product in the still bottoms.